As reported by Major Nelson, a new update for the Xbox 360 is now live.
Released to the preview program a couple of weeks ago and checked out here, this update adds support for USB hard drives of up to two terabytes in size. In addition there are a couple of small value added features such as being able to view your purchase history from the console.
I’m already finding the HDD support a very useful addition. I only wish it had arrived a couple of years earlier as it might have convinced me to spend money earlier on digital purchases.